1. Field of the Invention
This invention relates to piezoelectric transducers and particularly to those transducers in apparatus for determining the rate of flow of a fluid in which the propagation times of ultrasonic signals transmitted through the fluid are detected to determine flow rate.
2. Background Information
Ultrasonic transit time flow sensors, also known as “time of flight ultrasonic flow sensors”, detect the acoustic propagation time difference between ultrasonic signals transmitted upstream and downstream through a flowing fluid and process the time difference information to derive the fluid flow rate. The propagation time difference is usually very small and must be detected with high resolution and stability for the sensor to be practical. These sensors typically use piezoelectric transducer elements to generate and detect the acoustic signals. The acoustic coupling of these elements to the fluid, which is complicated by the need to attach electrical connections to the acoustically active transducer surfaces, is generally the major source of sensor instability and error. There is a long-standing need to minimize this problem in a practical and cost effective way.
In U.S. Pat. No. 6,739,203 Feldman et al. teach an approach to making time of flight transducers using piezoelectric ceramic elements in which a metallization layer on the piezoelectric ceramic is wrapped around an edge so that both of the two necessary electrical contacts can be made on the same side of the ceramic body.
In U.S. Pat. No. 6,822,376 Baumgartner describes a contacting arrangement for a piezoelectric element in which a metal mesh is clamped between a metallization layer on the piezoelectric and a metal contact pad on a circuit board.
In U.S. Pat. No. 6,570,300 Riedel et al teach the use of a mesh conductor that is adhered to a surface to make an electrical contact to a piezoelectric bender element.